Method and device for forming a pipe

ABSTRACT

A method and a device are proposed which accurately and efficiently form a pipe with a bending machine only without using any correcting means. A work having holes is fed into a bending machine in which under an upper roll, lower rolls parallel thereto are arranged and a pipe is formed with rough forming step and fine forming step. In the rough forming step, bending is done so that it will have a required diameter at the hole portions. In the fine forming step, the hole portions are not pressed for bending while the other portions are rolled so as to become closer to the required diameter to form the pipe.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a method and a device for forming apipe in which a plate with holes is formed into a completely circularpipe by means of a bending machine.

[0002] A method of forming a completely circular pipe by bending a steelplate by use of a bending machine has heretofore been carried out with abending machine in which one upper roll is vertically and horizontallymovably arranged over two lower rolls arranged parallel. The pipeforming method disclosed in JP patent publication 63-36852 is oneexample. This prior method comprises a preparatory of bending a centralportion, a main step and a step of bending both ends.

[0003] In the preparatory step of bending the central portion, the upperroll is lowered offset relative to the two lower rolls to a positionwhere frictional force necessary for the feed of the work is obtained.Thereafter, the upper roll is further lowered while pressing and bendingthe work for rolling until a predetermined arc necessary for the mainstep is obtained. After carrying out the main step in which rolling isfurther carried out with the predetermined arc, the both end bendingstep is carried out in which pressing/bending is applied to both ends ofthe work.

[0004] With this bending method, it is possible to bend a steel plateinto a U-shape using part of its working steps. One example of such amethod is proposed in JP patent publication 2000-288635. In thisU-bending method, after moving a steel plate clamped between the upperroll and the two lower rolls to a predetermined forming start position,the upper roll is lowered with a lowering amount divided into aplurality of portions so as to form a predetermined arc, while rotatingthe lower rolls in normal and reverse directions at rotating amountscorresponding to the lowering amounts to carry out multiple step formingwhile gradually narrowing each forming toward the minimum curvatureportion.

[0005] The bending methods by use of the bending machines described inthese two patent publications are used for flat plates in which no holesare formed. No mention is made about what influence the fact that holesare formed will have on the work accuracy if a hole is formed in theflat plate. If a pipe is actually formed by applying the bending methodof JP patent publication 63-36852 to a work with holes, it is known fromexperience that no normal bending is possible near the portions wherethere are the holes, and the radius of curvature partially decreases atsuch portions and the pipe is not made completely circular.

[0006] Thus in forming a pipe with holes, in order to obtain acompletely circular pipe, it has to be treated by one of the followingtwo methods. That is, the pipe forming method of JP patent publication63-36852 is applied without forming any hole in the work to form acompletely circular pipe, and thereafter, holes are formed atpredetermined positions by use of a drill. Otherwise, after a pipe hasbeen formed by applying this pipe forming method to one in which holeshave been formed in the work beforehand, bending is carried out againwith a different kind of press means to correct the curvature of thepipe, which is out of true at the hole portions.

[0007] But, simply by applying the pipe forming method of JP patentpublication 63-36852, it is impossible to obtain a completely circularpipe. If holes are formed with a drill after forming a completelycircular pipe, the pipe may become partially not completely circular dueto the influence of drilling. If a material formed with holes is formedinto a pipe, it may develop portions which are partially not completelycircular. Thus, it is necessary to carry out bending again at suchportions. Thus, extremely complicated steps are needed. So it isdifficult to obtain a completely circular pipe with a bending machinealone. A different kind of machine and step are needed for correction.

[0008] An object of this invention is to provide a method and a devicefor accurately and efficiently forming a pipe with a bending machineonly without using correcting means in uniformly bending a work withholes to a pipe diameter.

SUMMARY OF THE INVENTION

[0009] According to this invention, there is provided a method offorming a pipe comprising the steps of feeding a work having a holebetween an upper roll and a pair of lower rolls of a bending machine,the lower rolls being parallel to each other and relative to the upperroll, moving the work by the rotation of the lower rolls whilesupporting it with the upper and lower rolls, and forming a pipe bybending the work under pressure of the upper and lower rolls, whereinthe forming comprises a rough forming step in which the work is formedinto a pipe having a rough radius and a fine forming step followed bythe rough forming for finishing the pipe to a required radius, whereinin the rough forming step, the work is bent by pressing with the upperand lower rolls so that a required radius will be obtained at a holeportion, and in the fine forming step, no bending action is applied tothe hole portion and the work is rolled by pressing with the upper andlower rolls so that at portion other than the hole portion, the radiuswill coincide with that at the hole portion.

[0010] According to this invention, there is also provided a device forforming a pipe comprising an upper roll and a pair of lower rolls whichare parallel to each other and are arranged so as to vertically opposeeach other, one of the upper and lower rolls being provided so as to bemovable vertically and horizontally relative to the other, actuators forrotating, raising and lowering the rolls so as to move while supportinga work with holes which is supplied between the upper and lower rolls bythe rotation of the rolls, and simultaneously bend it under the pressureof the rolls to form a pipe, a control unit for controlling theactuators, the control including a control program for controlling apipe forming step comprising a rough forming step in which the work isformed into a rough radius and a fine forming step followed by the roughforming step for finishing it to a required radius, wherein in the roughforming step, the work is bent by pressing with the upper and lowerrolls so that a required diameter will be obtained at the hole portions,and in the fine forming step, no bending action is applied to the holeportion, and the work is rolled by pressing with the upper and lowerrolls so that portions other than the hole portions, the pipe radiuscoincides with that of the hole portions.

[0011] With the method and device for forming a pipe, simply byoperating a bending machine, without using any other auxiliary means orwithout needing troublesome auxiliary work, a finished product of a pipecan be formed by bending. In a method in which a pipe is formed bybending a work having holes, influences of pressing are differentbetween the hole portions and other portions. Thus, in the rough formingstep, bending is carried out such that the radius near the hole portionswill be a required radius, which is the radius of the pipe of thefinished product. The radius of the portions other than the holeportions is slightly larger than the required radius.

[0012] Thus, in the fine forming step, rolling is carried out onportions other than the hole portions to apply bending so that therequired diameter is obtained. Since the hole portions are alreadyworked to a required radius, by feeding the work with the upper rollseparated from the work, or supporting it with the upper and lower rollsso that bending action is not applied, and thereafter by lowering theupper roller and continuing rolling, the radius of the portions otherthan the hole portions approaches the required radius, so that a pipe ofa finished product is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Other features and objects of the present invention will becomeapparent from the following description made with reference to theaccompanying drawings, in which:

[0014]FIG. 1 is a block diagram of a control line with a perspectiveview of the bending machine embodying the present invention;

[0015]FIG. 2A is a view for explaining the rough pipe forming step;

[0016]FIG. 2B is a view for explaining the fine pipe forming step;

[0017]FIGS. 3A, 3B and 3C are flowcharts of rough pipe forming step;

[0018]FIGS. 3D and 3E are flowcharts of fine pipe forming step;

[0019]FIG. 4 is an explanatory view of fine pipe forming step; and

[0020]FIG. 5 is a view showing holes of a work.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] The embodiment of this invention will be described with referenceto the drawings. FIG. 1 shows a perspective view of the bending machineof an embodiment with a block diagram of a control circuit forcontrolling driving units (or actuators). This bending machine has anupper roll 1 arranged between opposed frames F, and two lower rolls 2and 2′ provided below the upper roll 1 so as to be parallel to eachother and relative to the upper roll 1. The upper roll 1 is provided soas to be moved up and down by a hydraulic cylinder 13 and to be movableback and forth by a motor 10.

[0022] The lower rolls 2 and 2′ are rotated in normal and reversedirections by a motor 6. While backup rolls and 2′ are provided belowthe lower rolls 2, they are omitted for simplicity. A hydraulic cylinder12 is provided to outwardly incline each frame F. In this embodiment, asthe actuators, the motors 6, 10 and the hydraulic cylinders 12, 13 areprovided.

[0023] The operation of the bending machine is controlled by a controlcircuit 5. It comprises a sequencer for carrying out control based onsignals from a numerical setter 5 s. A numerical setter 5 a is forsetting rotating amounts Z (Z1, Z2 . . . ) of the lower rolls 2, 2′,which are converted to moving amounts of a work W. A numerical setter 5b is for setting vertical movement amounts Y (Y1, Y2, . . . ) of theupper roll 1, and a numerical setter 5 c is for setting horizontalmovement amount X of the upper roll 1.

[0024] For these set values Z, Y and X, values set at the numericalsetters 5 a-5 c based on bending parameters such as the yield point ofthe material, plate thickness, plate width, radius of curvature R andthe size and position of the holes are input into the control circuit 5beforehand. The numbers of revolutions of the lower rollers 2 and 2′ aredetected by signals from rotation sensors 7 and are converted todistance L in the control circuit 5.

[0025] Vertical movement of the upper roll 1 is carried out by feedinghydraulic pressure to the hydraulic cylinder 13 by a hydraulic pressurecontrol circuit 8. The amounts of its vertical movement are detected bya position detector 9 mounted on a side frame F. The horizontal movementof the upper roll 1 is detected by a position detector 11 mounted on alower frame. Operations of the motors 6 and 10 and the hydrauliccylinders 13 and 12 are controlled based on commands from the controlcircuit 5. Detected values of the position detectors 9 and 11 and therotation sensors 7 are input to the control circuit 5.

[0026] The method of forming a pipe by bending by means of this bendingmachine will be described below with reference to FIGS. 2A and 2B andthe flowcharts of FIGS. 3A-3E. When a start button of the bendingmachine is pressed, the control circuit will begin control based onsignals from an input device, selected beforehand from among controlmodes by an operator. In this control action, the operation conditionsat the start are checked, and if there should be any abnormality,“abnormal message” is displayed.

[0027] If there is no abnormality, it is determined that preparation forworking has completed, and the actions shown in FIG. 2A and thesubsequent figures will begin. First in step S1 of FIG. 3A, the backuprolls (not shown) are moved up or down, and in step S2 it is judgedwhether the backup rolls are at predetermined position H1. After astopper 3 for the work W (steel plate) has been raised in step S3, asshown in FIG. 2A(a), the work W is fed from the rear lower roll 2′toward the front lower roll 2 into between the upper roll 1 and thelower rolls 2, 2′ and the work W is held with its front end abutting thestopper 3, which is arranged so as to be parallel to the lower rolls 2and 2′. Also, before the start of operation, the upper roll 1 is at astandby position Y0 which is above the lower rolls 2, 2′.

[0028] In response to the work feed end signal, the upper roll 1 islowered to position YL (not shown) in step S5. In step S7, the upperroll 1 is moved from standby position X0 to position X1 toward the rearlower roll 2′. In S9, the upper roll 1 is lowered to set position Y1 toclamp the work W (see FIG. 2A(b)). In S11, the lower rolls 2, 2′ aredriven to move the work W so that the front end of the work W will cometo a position right over the front lower roll 2 and spaced a distance Z1from the stopper 3 (FIG. 2A(b)). The values X1, YL, Y1, Z1 are valuescalculated according to the bending mode beforehand and stored in thecontrol circuit 5. The step automatically proceeds to the next operationafter the work arrives at the set position.

[0029] The below-described Y2, Y3 . . . , Z2, Z3 . . . etc. are alsovalues calculated and set according to the bending mode. In the state ofFIG. 2A(b), the upper roll 1 is still set at position Y1 where the workW is retained in a horizontal state. In this position, no bending actionis given to the work W. This completes the setting of the work W to theforming start position. After lowering the stopper 3 in S13, the lowerrolls 2, 2′ are driven in S14 to move the work W forward to startforming and feed it to set position Z2. Simultaneously with the start offorming, as shown in FIG. 2A(c), in S16, the upper roll 1 is lowered toset position Y2-θ. The work is subjected to bending under the pressingforce by the upper roll.

[0030] Driving of the lower rolls 2, 2′ and lowering of the upper roll 1are started substantially simultaneously. Y2 is a value necessary forkeeping the upper roll 1 at set position in FIG. 2A(f). In the state ofFIG. 2A(c), the upper roll 1 is set at set position Y2-θ which is justbefore the set position Y2.

[0031] While the work W is being fed to set position Z2 in step S15, ittakes time for the upper roll 1 to lower to set position Y2-θ. Bendingduring this time is in a spiral form because the position of the upperroll 1 changes little by little. By further bending after the upper roll1 has lowered to set position Y2-θ, an R′ portion is formed with theradius R′. But a portion of a predetermined short length from the frontend of the work W is left unworked. Thus, in S18, as shown in FIG.2A(d), the upper roll 1 is lowered to set position Y3 (in S19) to carryout press end bending. Bending up to the length Z2 thus ends.

[0032] Next, the entire circumferential length of the work W is formedinto a pipe of a desired radius R (R>R′) by reversing the feed directionof the work W as shown in FIG. 2A(e). First, from the state of FIG.2A(d), in S22, while raising the upper roll 1 to set position Y2-α, thelower rolls 2, 2′ are driven in step S20 in the opposite direction toset position γ. This is done to stabilize the work W on the lower rolls2, 2′ while the upper roll 1 is being moved to set position X2 in thebelow-described step S24.

[0033] After raising the upper roll 1 to set position Y2-α, in step S24shown in FIG. 3C, the upper roll 1 is moved in the opposite direction toset it in set position X2 as shown in FIG. 2A(e). After setting theupper roll 1 in the above position, the upper roll 1 is lowered in S26to set position Y2, and the lower rolls 2, 2′ are again driven in S28 inthe opposite direction to feed it to set position Z3 (in S29).

[0034] When the radius R′ portion, spiral portion and straight portionpass, bending to a desired radius R is done by the upper roll 1 which isset at position Y2 and the lower rolls 2, 2′. Further, in the samemanner as in S18, press end bending is done for a portion of apredetermined short length from the opposite end by lowering the upperroll 1 to set position Y3 in S30. Thus, as shown in FIG. 2B(g), a pipeof the desired radius R is formed over the entire circumference of thework.

[0035] This is a rough forming step carried out by bending the work W.This bending of the work W is working to a desired radius R. The radiusR is slightly larger than the radius R0 of a pipe as the finishedproduct to be ultimately obtained (R0<R). The reason is that as shown inFIG. 4, at portions near holes h of the work W, the influence of bendingis stronger than at portions other than the portions near the holes, sothat the radius will be smaller than at other portions and thus a pipehaving a uniform radius will not result. Thus, work is done such thatonly the portion at the holes h will have the radius R0 of the finishedproduct.

[0036] In FIGS. 2A(c) and 2A(f), which show the rough forming step, thereason why the vertical position of the upper roll 1 is set at (Y2-θ)and Y2 is as follows. As shown in FIG. 4A, while bending the work Wduring rolling in the going path, as described above, the straightportion, spiral portion and radius R′ portion are formed with the upperroll 1 set at Y2-θ, so that the radius of the portions near the holeswill be R0′ which is smaller than at other portions. As shown in FIG.4B, bending is carried out with the position of the upper roll 1 set atY2 in the rolling in the return path so that the radius at the holeportions will be the radius R0 of the finished product.

[0037] In the rolling in the going and return paths, the contact pointsbetween the upper roll 1 and the lower rolls 2, 2′ are T1, T2 and T3.The way the work W contacts the upper and lower rolls 1, 2, 2′ remainsunchanged until the work W reaches the state of FIG. 4B. But when thework W further moves in the direction of the arrow beyond the state ofFIG. 4B, since the radius R0′ at the hole portions h is different fromthe radius at the other portions, the way which they contact at T2 andT1 changes, so that slip occurs between the work W and the upper roll 1.

[0038] In order to eliminate such a slip, the position of the upper roll1 in the going path is set at Y2-θ, which is slightly above the positionY2 in the return path, so that the pressure by the upper roll 1 will begreater in the return path than in the going path, thereby smoothlyrolling while preventing slip. Thus, by setting the position of theupper roll 1 at Y2 for the rolling in the return path, the bendingradius R0′ of the portions at hole h in the going path will be the piperadius R0 of the finished product, and the other portions will have aradius R which is slightly greater than R0.

[0039] After the rough forming, as shown in FIG. 2B(h), the upper roll 1is returned to the set position Y2-α and to the central position betweenthe lower rolls 2, 2′. At this position, no load is applied on the workW. In order to return it to this set position, the upper roll 1 israised in S34 to set position Y2-α, and the lower rolls 2, 2′ areslightly driven in S32 to feed them to set position γ so that the work Wwill be in a stable state on the lower rolls 2, 2′. And in S36 in FIG.3D, the upper roll 1 is returned to the central position.

[0040] Next, in the fine forming step in FIG. 2B(i) and subsequentfigures, bending is carried out so that the work will have the radius R0as the pipe of the finished product. In S38, the lower rolls 2, 2′ aredriven to return the work W to a predetermined position, and in S40, theupper roll 1 is lowered to set position Y4. At this time, steps S40, S41and steps S38, S39 are parallelly carried out. Thereafter in S42, thelower rolls 2, 2′ are driven to feed the work W to set position Z4(Z4-1+Z4-2+Z4-3), and the bending in the first fine forming step iscarried out. Thereafter,in the same manner, the lowering of the upperroll 1 and the feed of the work W by means of the lower rolls 2, 2′ arerepeated three times to move the work to Y5 in S44, to Z5 in S46, to Y6in S48 and to Z6 in S50.

[0041] Details about feed to set positions Y4, Y5 and Y6 and setposition Z4, Z5 and Z6 are shown in FIG. 2B(i) and the flowchart of FIG.3E. In S421, the lower rolls 2, 2′ are driven to feed the work W to setposition Z4-1. As shown in FIG. 2B(i), this position is a position justbefore the upper roll 1 reaches the holes h. At this set position, asshown in FIG. 2B(j), the upper roll 1 is raised in S422 to set positionY4-β, the lower rolls 2, 2′ are driven in S423 to feed the work W to setposition Z4-2. After passing the holes h, the upper roll 1 is loweredagain to set it at position Y4. Thereafter, in S425, the lower rolls 2,2′ are driven to feed the work W to Z4-3 to carry out bending over theentire circumference. After carrying out the first fine forming in thismanner, the work W is turned in the opposite direction to carry out thesecond fine forming with the upper roll 1 set at the position Y5. Nextthe work W is reversed to carry out the third fine forming with theupper roll 1 set at position Y6.

[0042] While an example in which the fine forming is carried out threetimes has been described, the number of fine formings may be more thanor less than three. In any fine forming, the upper roll 1 is raised alittle not to carry out bending near the holes h, and at any otherportions the upper roll 1 is lowered little by little as the number offine formings increases, to obtain the pipe radius R0 for the finishedproduct. Also, the set position for fine forming and the number ofrisings and lowerings at the hole portions may be changed according tothe number of holes.

[0043] As shown in FIG. 5, if the work W has holes hL and hS havingdifferent diameters, handling should be made so that the hole HL, whichis larger in diameter, corresponds to the above-described hole h becausethe influence of the hole hS, which is smaller in diameter, is smallerthan that of the larger-diameter hole hL.

[0044] As described above in detail, in the method and device forforming a pipe by bending a work having holes according to thisinvention, in the rough forming step, the hole portions are formed to arequired radius while the other portions are formed to a slightly largerradius. In the fine forming step, pressing for bending is not done atthe hole portions while the other portions are brought to a requiredradius by rolling little by little. Thus, simply by operating a bendingmachine, the work can be finished to a finished product without the needof correcting work using other auxiliary means. Thus, a pipe can beformed accurately and efficiently by use of only a bending machinewithout troublesome work.

1. A method of forming a pipe comprising the steps of feeding a workhaving a hole between an upper roll and a pair of lower rolls of abending machine with said lower rolls being parallel to each other andrelative to said upper roll, moving the work by the rotation of saidlower rolls while supporting it with said upper and lower rolls, andforming a pipe by bending the work under pressure of said upper andlower rolls, wherein the forming step comprises a rough forming step inwhich the work is formed into a pipe having a rough radius and a fineforming step followed by said rough forming for finishing the pipe to arequired radius, wherein in the rough forming step, the work is bent bypressing with said upper and lower rolls so that a required radius willbe obtained at a hole portion, and in the fine forming step, no bendingaction is applied to said hole portion and the work is rolled bypressing with said upper and lower rolls so that at portion other thansaid hole portion, the radius will coincide with that at said holeportion.
 2. A method of forming a pipe as claimed in claim 1 wherein ifa work having holes of different sizes is formed into a pipe, the workis formed into a pipe with the larger-diameter hole regarded as saidhole of the work and the smaller-diameter hole portion regarded asportion other than said hole portion.
 3. A method of forming a pipe asclaimed in claim 1 wherein said rough forming step comprises the stepsof feeding the work while pressing it between said upper and lower rollswith said upper roll shifted to one side from the center between saidlower rolls to roll the work, and pressing for end bending at one end ofthe work in a going path, then returning the work while pressing itbetween said upper and lower rolls with said upper roll shifted to theother side to roll the work, and pressing for end bending at the otherend of the work in the return path.
 4. A method of forming a pipe asclaimed in claim 3 wherein in said rough forming step, every time theworking in the return path is carried out, the distance between saidupper roll and said lower rolls is reduced in a stepwise manner so thatthe radius of the finished product will be obtained at the hole portionof the work.
 5. A device for forming a pipe comprising an upper roll anda pair of lower rolls which are parallel to each other and are arrangedso as to vertically oppose each other, one of said upper and lower rollsbeing provided so as to be movable vertically and horizontally relativeto the other, actuators for rotating, raising and lowering said rolls soas to move while supporting a work with holes which is supplied betweensaid upper and lower rolls by the rotation of the rolls, andsimultaneously bend it under the pressure of the rolls to form a pipe, acontrol unit for controlling said actuators, said control including acontrol program for controlling a pipe forming step comprising a roughforming step in which the work is formed into a rough radius and a fineforming step followed by said rough forming step for finishing it to arequired radius, wherein in the rough forming step, the work is bent bypressing with said upper and lower rolls so that a required diameterwill be obtained at the hole portions, and in the fine forming step, nobending action is applied to the hole portion, and the work is rolled bypressing with said upper and lower rolls so that portions other than thehole portions, the pipe radius coincides with that of the hole portions.6. A device for forming a pipe as claimed in claim 5 wherein said upperroll and said lower rolls which are parallel thereto and parallel toeach other are arranged.
 7. A method of forming a pipe as claimed inclaim 2 wherein said rough forming step comprises the steps of feedingthe work while pressing it between said upper and lower rolls with saidupper roll shifted to one side from the center between said lower rollsto roll the work, and pressing for end bending at one end of the work ina going path, then returning the work while pressing it between saidupper and lower rolls with said upper roll shifted to the other side toroll the work, and pressing for end bending at the other end of the workin the return path.